Throughout this application, various publications are referenced. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosure of these publications is hereby incorporated by reference into this application to describe more fully the art to which this invention pertains.
Approximately 60% of newly diagnosed patients with prostate cancer will have established metastasis at the time of diagnosis (2). Once the disease has spread to distant rites, the overall prognosis is poor (3,4). Organ-confined prostate cancer should be curative upon removal of the gland, however screening modalities to assess early metastases often fail to identify a significant subset of patients with locally invasive disease (involving penetration of the capsule or seminal vesicle). Recent studies report that up to 40-50% of patients who were thought to have clinically localized disease were found to be understaged subsequent to radical surgery (5,6,7). This failure rate creates a clinical dilemma since operative therapy is not the appropriate treatment modality for these patients. Clearly, development of a more sensitive means to identify patients with micrometastic, locally invasive disease is warranted.
Prostate cancer metastases are more frequently found in the pelvic lymph nodes and on bone and these are sites surveyed most aggressively in patients diagnosed with prostate cancer. The involvement of draining lymph nodes in the dissemination of this cancer is expected, given our understanding of solid tumor behavior. The means by which the prostate cancer cells target the bone is debated, but suspected to involve blood vessels to the lower spine, specifically the vertebral venous plexus (8,9). This spread presupposes that prostate cancer cells are shed into the blood stream and implies a role for hematogenous dissemination in prostate cancer progression.
Indeed, a preliminary study showing that prostate cells can be putatively identified in blood specimens of patients with metastatic prostate cancer supports the concept of blood-borne metastasis (10).
This previous study reported that cells synthesizing prostate specific antigen (PSA) were present in the circulating blood of patients with prostate specific antigen (PSA) were present in the circulating blood of patients with prostate cancer metastases. Since the expression of this protein is restricted to epithelial cells of the prostate gland, the detection of PSA synthesizing cells in the circulation indicates an unexpected and potentially abnormal situation. Here, we describe our development of an extremely sensitive "enhanced" PCR-based assay that allows us to identify PSA-synthesizing cells even when they are highly diluted in a population of peripheral lymphocytes. When this assay was applied to RNA extracted from peripheral blood cells of prostate cancer patients, it enabled us to distinguish the overwhelming majority of patients with overt metastatic disease as well as patients with locally invasive tumors that were understaged by conventional screening modalities (i.e. digital rectal exam, CT-scan and/or endorectal MRI). The remarkable accuracy of this assay in upstaging patients with apparent clinically localized disease could eliminate a significant number of prostate cancer patients from unnecessary operations and potentially increase the cure rate in patients who are treated by radical prostatectomy. Since this simple assay involves the molecular detection of a prostate-specific gene product, it represents the first reported instance of molecular staging of a solid human tumor.